MEDICAL SCIENCE: Delusion, Benign and Bizarre, Is Recognized as Common

By DANIEL GOLEMAN

Published: June 27, 1989

DELUSIONS are more commonplace than most people assume, a growing number of researchers are concluding. These researchers say the delusions of those with psychiatric disorders are fundamentally no different from, say, a private belief that a color is unlucky or popular beliefs in the existence of flying saucers.

By tracing how delusions develop, researchers hope to find ways to identify people most at risk of mental illness and stop their delusions from developing into full flower even though the disorder is one of the most difficult to treat.

A belief is considered a delusion if a person holds to it no matter how bizarre it is and despite all evidence to the contrary. A belief that flying saucers exist is considered benign, while the belief that a person has been contacted by people on flying saucers is worrisome. Some researchers say most people have minor delusions of one kind or another.

''About four in a hundred people have extremely deviant beliefs,'' said Loren J. Chapman, a psychologist at the University of Wisconsin, who is conducting a study of how delusions develop. ''Some of these people might seem strange to just about anyone, while others are doing very well, with their unusual beliefs limited to isolated topics.''

The researchers say people who develop such severe delusions tend to stop searching for alternative explanations far sooner than do most other people. Hearing Thoughts

Dr. Chapman is testing the hypothesis that those who hold the most deviant beliefs are at risk for mental illness.

One woman studied by Dr. Chapman insisted that people could read her mind from the expression on her face. That belief, and others like it, led Dr. Chapman to predict that the woman, though living a normal life, was at risk for mental illness.

Indeed, when interviewed two years later, she said people heard her thoughts, a delusion that was part of a psychosis she had developed.

In themselves, delusions are benign, the experts say. ''The trouble starts when those beliefs gain such intense emotional importance we feel compelled to act on them,'' said Dr. Hugh Hendrie, chairman of the department of psychiatry at the Indiana University School of Medicine. Order and Meaning

Dr. Brendan Maher, a psychologist at Harvard, has put forward the most influential theory about delusions, proposing that they spring from quite ordinary ways of thinking. In his view, delusions are like other beliefs, in that they give order and meaning to what is otherwise a puzzle in life.

''Puzzles demand explanation; the search for an explanation begins and continues until one has been devised,'' said Dr. Maher.

For instance, a strange sound in the night might be caused by a cat, but a deluded person might assume it was caused by a burglar even if such an explanation was implausible.

''One of the assumptions we make in thinking about delusions is that implausible explanations are rather rare; but I argue they are rather common,'' said Dr. Maher, who this week became dean of the Graduate School of Arts and Sciences at Harvard. Self-Confirming Beliefs

''The standard of rational, deductive thinking does not apply to normal thought,'' Dr. Maher said. ''Many or most people privately hold strange beliefs that could be diagnosed as delusional if brought to the attention of a clinician.''

Explanatory beliefs tend to be self-confirming in that contradictory data are ignored, while anything that might support the theory is given prominence. That, Dr. Maher says, has been shown to be the case with ordinary beliefs as well as with people who develop delusions.

Dr. Maher's theory is set forth in ''Delusional Beliefs'' (Wiley), a book he edited with Thomas Oltmanns, a psychiatrist at the University of Arizona. Culture and Community

In evaluating whether a belief is a delusion, clinicians take into account the background of the beliefs in a person's culture, community or peer group.

''If you say someone is controlling your thoughts, that may or may not be an outright delusion,'' Dr. Chapman said. ''For instance, if you think that God is controlling your thoughts - say making you study instead of going out to a movie - and you are a pious person, that belief has cultural support; it's not a deviant belief.''

''But if you believe the Devil is making you think bad thoughts, and you do not, for instance, hold to a religion with such a view, then that's a more deviant belief,'' he said. ''And it you believe your uncle in Chicago is making you think evil thoughts, then that's more deviant still.''

There are more than 70 different clinical conditions in which delusions can occur, including brain tumors, alcohol intoxication, epilepsy and senility. Delusions are among the prominent symptoms of disorders like manic-depression, schizophrenia and ''delusional disorder,'' which formerly was known as paranoia.

Of these, delusions are the principal symptom only in delusional disorder, in which people are typically coherent and functioning well in other areas of their lives. They will be convinced, for instance, that movie stars are in love with them and sending them covert messages through pointed lines and looks in a film.

Delusions that are symptoms of other problems usually clear up when the underlying mental disorder is treated, Dr. Hendrie said.